1. Field of the Invention
This invention relates to an improved sound reproduction device particularly useful for talking books and the like. More specifically, it relates to a sound reproduction device which can be used for reproducing sound recorded on an optical sound track printed on an opaque surface. The device is particularly useful in conjunction with "talking books" such as children's books, dictionaries, and language texts, which are adapted to include printed optical sound tracks for illustrative sound effects or as pronunciation guides.
2. History of the Art
Optical sound recording and reproduction is one of the most promising approaches to the development of commercially viable "talking books" capable of supplementing written text with recognizable sound. The advantage of this approach is that the text and the optical record and be printed simultaneously using conventional printing techniques. Magnetic recording, in contrast, requires the use of magnetic materials, separate application and recording, and, in some instances, the use of magnetic shielding materials to prevent cross-coupling between adjacent tracks.
While optical sound recording has been known for many years, presently available optical reproduction heads are not well suited for manual operation. Optical sound systems using stationary reproduction devices have been used for many years in the motion picture industry. Such systems typically involve modulation of a light beam transmitted through a moving optical track. Specifically, the sound track is photographically recorded on the film as an optical track comprising a narrow strip of variable optical density or variable transparent area. During projection, the film is passed between a light source and a photocell so that the optical track modulates the intensity of the light reaching the photocell, and the thus-modulated output of the photocell is amplified and applied to a speaker where it is converted into sound.
U.S. Pat. No. 2,369,572 issued to H. E. Kallman proposes the use of printed optical tracks in talking books. It does not, however, describe the sound reproduction device to be used with these books.
U.S. Pat. No. 2,018,200 issued to Fernando Crudo describes a sound reproduction device to be used in playing sound records of the type disclosed therein. In this arrangement, the sound is reproduced by reflecting light from the track directly into a photocell connected to a speaker. Such an arrangement is not, however, well suited to manual operation as is desired for talking books.
For good results using manual operation, it is desirable to demodulate the light reflected from strips of the optical track which are relatively narrow in the direction of pick up device translation and relatively long in the transverse direction. The strips are desirably narrow in order to achieve good frequency response and desirably long in order to permit the use of a relatively wide optical track which can be manually followed.